Questions Being Addressed
The Mayo Mammography Health Study (MMHS) research team is attempting to address four main questions:
1. Can features on a mammogram be used to help determine a woman's risk of breast cancer?
Women have mammograms to detect breast cancer or high-risk lesions in the breast. But the MMHS research team is interested in using mammograms for more than cancer screening.
Researchers in the study examine features on mammograms that might help identify groups of women who are at higher or lower risk of developing breast cancer in the years after their mammograms.
The features of interest reflect variations in the amount and location of dense breast tissue vs. fatty breast tissue, viewed as differences in the light and dark regions on the mammogram image. Researchers also review how these features might change with age and therapy.
Two of the features on mammogram images that researchers are examining for their importance in future breast cancer are:
- Breast density
- Patterns of breast density
Images show breasts with different amounts of dense tissue on the mammogram. The mammogram on the right shows a fatty breast, and the mammogram on the left shows a dense breast.
Computerized algorithm (Cumulus) for estimating percent of breast density. The red line notes the outline of the breast, and the green line notes the outline of dense tissue.
Breast density is the term used to describe the variation in dense tissue on a mammogram image.
Fatty breast tissue is radiologically more translucent than is dense (fibroglandular) breast tissue. This means that regions of a breast that comprise fatty tissue will appear darker on a mammogram image, while regions that comprise mainly dense tissue appear whiter.
Breast density can be classified in many ways, including the overall amount or proportion of dense tissue on the mammogram. The Mayo Mammography Health Study uses the clinical density measure, the American College of Radiology Breast Imaging Reporting and Data System Atlas (BI-RADS) density, and computerized measures to assess the percentage of density.
The MMHS research team has shown that for the same age and weight, women with increased breast density have a higher risk of developing breast cancer.
Pictures of mammograms with similar percent densities that show different patterns and variation of breast density.
Patterns of density
The amount or percent of dense tissue on a mammogram may not be the only aspect of the mammogram that provides information about a woman's future breast cancer risk. Patterns of density may also play a role in breast cancer risk.
Two breasts can have the same percent density, but the dense tissue can be distributed in different patterns throughout the breast. For example, some breasts might show a central area or cluster of dense tissue, while others have several areas of dense tissue scattered throughout the breast. MMHS research has shown that the variant in the tissue on the mammogram also is a risk factor for breast cancer.
2. Do changes in breast density over time influence breast cancer risk?
A series of mammograms taken from the same woman over the course of 10 years shows differences in the amount and proportion of dense tissue over time.
Example of a change that can occur in some women when they take hormones for postmenopausal symptoms. The mammogram on the left is from a woman before taking postmenopausal hormones. The mammogram on the right was taken from the same woman one year after she started hormones. This woman experienced a dramatic increase in breast density corresponding to her use of hormones. Whether this increase places a woman at an increased risk of breast cancer is unknown.
Breast density is not a static trait. Breast density changes with age, for example. On average, older women have lower density breast tissue than do younger women. The greatest change in density occurs during the menopause years. Breast density also changes with certain types of hormone therapies, such as hormone treatments for menopause.
The MMHS research team is examining how women's breasts change in density over time, what underlies these changes and whether these changes are associated with the risk of developing breast cancer.
Because a lower breast density is associated with a lower risk of breast cancer, it is hypothesized that decreasing density over time will result in decreased cancer risk compared with women whose breast density increases or stays the same.
Mayo Mammography Health Study researchers have published the first data to show that breast density on the mammogram correlates with involution in the breast. Age-related lobular involution, or physiological atrophy of the breast, is a process in which there is a reduction in the number and size of the acini per lobule and replacement of the intralobular stroma with dense collagen and, ultimately, fatty tissue. This is important for understanding what breast density on the mammogram represents at the level of the tissue.
3. Is breast density a risk factor for all types of breast cancer?
There are many types of breast cancer, including in situ cancer, invasive cancer, cancers that differ on the presence or absence of certain receptors (estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2), and even cancers that differ by tumor characteristics, such as grade, nodal involvement and size.
While increased breast density is a risk factor for breast cancer, it's not clear whether breast density is a risk factor for all types of breast cancer.
The Mayo Mammography Health Study research team is leading a consortium to investigate whether breast density is a risk factor for all types of breast cancers or only certain types. Because large numbers of women are needed to examine specific and sometimes rare types of breast cancer, the researchers formed a collaboration with researchers at both the University of California San Francisco and Harvard University to address this question.
4. Is breast density influenced by genetics?
Even though higher breast density is one of the strongest risk factors for breast cancer, there is little understanding about how breast density might influence breast cancer.
Identifying genetic variation associated with breast density could provide clues to better understand the relationship between breast density and breast cancer. Ultimately, this might lead to better identification of those with breast cancer, and improved prevention and treatments for breast cancer.